The CNN story says "Nine out of every 10 people on the planet breathe air that contains high levels of pollutants and kills seven million people each year, according to a new study from the World Health Organization."

Sounds frightening and it should. A significant portion of people alive today live with air pollution levels which are close to or exceed the WHO Air quality guidelines. These people predominantly live in developing countries or countries classified as "low or middle income."

But the quote doesn't tell the whole story. What constitutes a high level? What is a pollutant? And why are millions of people dying from exposure?

The new study specifically addresses an update to the WHO Global Urban Ambient Air Pollution Database. It starts by pointing out 80 per cent of people living in urban areas where air pollution levels are monitored are exposed to levels above the guidelines.

It goes on to specifically focus on two forms of particulate air pollution called "PM 10" and "PM 2.5."

These are tiny particles which enter the lung and have been linked to heart disease, stroke, lung cancer and both chronic and acute respiratory diseases. It is PM 2.5 or particulate matter less than 2.5 microns in size which are particularly troubling as they can penetrate deep into the lungs right down to the cellular level. The tiny particles are not filtered out by the cilia lining our respiratory pathways. Nor are they necessarily caught in and expel with our mucus.

The particles are so fine, they can penetrate the bronchioles or alveoli. For asthmatics, these particles can trigger an attack, which is why Prince George sometimes has air quality advisories.

But more troubling from a health perspective is the relationship between the density of particles in the air and lung cancer. In a study of over 300,000 individuals, researchers determined that for every 10 microgram/cubic metre increase in PM 2.5, there is an accompanying 36 per cent increase in the likelihood of lung cancer. Or put another way, the number of deaths due to lung cancer is about twice as high at 35 micrograms per cubic metre as at 10.

The WHO Guidelines set 25 microgram per cubic metre as the acceptable 24 hour exposure and 10 micrograms per cubic metre as the annual mean. Anything above these levels are considered "high" by the WHO standards.

Furthermore, there is no safe or acceptable level for exposure to particulate matter. Most substances have a lower limit below which they will not have detectable adverse effects on the human health but particulate matter seems to be one of the compounds where there is no such thing as a safe dose.

Where do these particles come from?

There are a number of sources and the majority are not industrial. Perhaps the single largest source worldwide is the combustion of organic matter. Cigarette smoke is rife with particulate matter. It is these tiny particles which give rise to its distinctive blue haze. Marijuana smoke is equally polluted and just as dangerous from a cancer-causing perspective.

Wood smoke, from home fireplaces and stoves, is another significant source of particulate matter. As are campfires and backyard bonfires. If you can see or smell smoke, you are pretty much assured of breathing in particulates.

The largest source of particles, though, is cooking and household lighting. WHO estimates 40 per cent of the people in the world use combustion of organic matter - wood, coal, animal dung and such - as fuel for cooking and lighting. The conveniences of our modern age are not evenly spread through the world's population which is why economically disadvantaged countries have worse health outcomes.

There are large cities where a particulate haze hangs persistently in the air. Industrial sources only account for a fraction - one third to one half - with the remainder divided equally between transportation and household sources.

Prince George is actually blessed with relatively clean air. Our annualized PM 10 levels are 15 micrograms per cubic metre which are below the 20 micrograms per cubic metre levels set by WHO. Our annualized PM 2.5 is 9 micrograms per cubic metre which is close to the limit but definitely on the low end of cities worldwide.

Indeed, Prince George is 2,433rd out of 2,975 cities around the world.

This is one time being last would be a good thing.

We could be doing more to clean up our local air. For example, finding ways to eliminate diesel emissions from chip hauling trucks would be a good start. Maybe when Tesla starts manufacturing electric big rigs at marketable prices, we could use some of the carbon tax revenues collected by our government to offset the costs of fleet conversions. It would certainly improve our local air quality and cut down on greenhouse gas emissions at the same time.

In the meantime, particulate emissions will remain a hazard for the majority of the world's population.

• The Surgeon General has determined that there is no safe level of exposure to ambient smoke!

• If you smell even a subtle odor of smoke, you are being exposed to poisonous and carcinogenic chemical compounds!

• Even a brief exposure to smoke raises blood pressure, (no matter what your state of health) and can cause blood clotting, stroke, or heart attack in vulnerable people. Even children experience elevated blood pressure when exposed to smoke!

• Since smoke drastically weakens the lungs' immune system, avoiding smoke is one of the best ways to prevent colds, flu, bronchitis, or risk of an even more serious respiratory illness, such as pneumonia or tuberculosis! Does your child have the flu? Chances are they have been exposed to ambient smoke!